there are a few ways to race the half marathon distance, which we can discuss as you get closer to the event

however, in preparation for the distance and especially if you have the 5 x 2k session under control, you could consider increasing your long run to 20k. Ideally, you should be looking to develop towards 25k over time, to gain the benefits from aerobic development. We can do this in steps, but good to mention now.